This invention relates generally to turbomachinery blading and, more particularly, to an air-cooled turbine blade or stator nozzle having an impingement baffle disposed therein for impinging cooling air on the internal blade airfoil wall. The invention herein described was made in the course of or under a contract, or a subcontract thereunder, with the United States Department of the Air Force.
In order to obtain satisfactory performance of gas turbine engines it has been necessary to increase the maximum turbine operation temperatures to levels which are significantly higher than the melting point of available blade materials. Consequently, high pressure turbine blades of all modern gas turbines must necessarily be cooled to lower temperatures to enable them to perform their functions for a required engine life. A common method by which the blades are cooled is to bleed air from the compressor and deliver it to the turbine either internally of the engine through passageways formed by the turbine and compressor rotor shafts and discs or through piping mounted externally of the engine.
One of the most effective methods of cooling turbine rotor blades and turbine stator nozzles is that of impinging cooling air on the inner walls thereof by means of an impingement baffle inserted into the hollow airfoil. The impingement baffle which is formed in substantially the same shape as the inside of the airfoil is spaced from the airfoil inner walls by a distance commonly known as the impingement distance. Cooling air is forced into the internal recess of the baffle, and then passes through a plurality of small holes in the baffle walls to impinge on the internal walls of the airfoil in a high velocity rate, thereby resulting in high efficiency cooling of the blade airfoils.
The impingement distance is critical in the design of the combination to the extent that the proper airflow distribution and velocity is desired. A common method of controlling the impingement distance is to form a plurality of dimples which protrude outwardly from the baffle walls and frictionally engage the inner walls of the blade. In addition to establishing impingement distance, the dimples also serve to position and support the baffle. A problem arises, however, when the dimples begin to wear thin because of vibration and thermal movement of the insert. Since the baffles are composed of a material which is necessarily light in weight, exhibits high strength capabilities, and is resistant to high temperatures, they tend not to demonstrate good wear characteristics. The integrally formed dimples in the baffles have a minimal contact area and, consequently, tend to wear thin resulting in fatigue cracks which creep from the thin dimple surface to a point of failure in the baffle.
It is, therefore, an object of this invention to provide a turbomachine blade which will operate in an environment of high temperature and high speed movement without resultant failure.
Another object of this invention is to provide a turbine blade baffle insert which is not susceptible to significant vibrational movement within the turbine blade cavity.
A further object of this invention is the provision for a turbine blade insert which is economical to manufacture, effective in use and extremely functional in use.
These objects and other features and advantages will become more readily apparent upon reference to the following description when taken in conjunction with the appended drawings.